Sarah Shadlock makes her first appearance in The Silkworm, at Matthew’s mother’s funeral. She is a friend of Matthew’s from their university days, and she is first seen embracing Matthew in a way that Robin thinks is “a little more lascivious, perhaps, than was appropriate in the circumstances.”
In Career of Evil, after socializing with Sarah and her boyfriend, Tom, it is observed that Robin and Matthew always seem to quarrel. Robin regards Sarah as a “shit stirrer,” who at university “had tried as hard as she could to win Matthew away” from her.
Physically, Sarah is described as looking like Strike’s girlfriend Elin, with Nordic-blonde beauty (but Sarah’s not as beautiful as Elin, in Robin’s estimation).
In Lethal White, we learn that Sarah is recently engaged to Tom Turvey. Still disliked by Robin, Sarah continues in her flirtatious attitude with Matthew and general “shit stirring” that Robin has previously referred to. Sarah and Matthew often team up to tease Tom about his baldness, which Tom is very subconscious of.
We also learn that Sarah works for the auction house, Christie’s. A fact that later comes in handy for Robin to gain information on art during the Chiswell investigation.
In the TV series adaptation, Sarah is portrayed by actress Antonia Kinlay.